Alexanderson Day on July, 3'rd!

For all of us loving the odd transmissions, one important date to mark in your calendars is July 3'rd 2011, the Alexanderson Day, where worlds only intact and working alternator type radio transmitter, Alexanderson Alternator (SAQ) is once again switched on at 9:00 UTC and 12:00 UTC, transmitting CW on 17.2kHz.

(picture linked from Wikipedia page)

The transmitter at Grimeton, Sweden, is a spectacular piece of equipment representing a true (and still working!) heritage of the very early days of radio. Its first transmission took place in October, 1924 and it has been air-worthy ever since. After the WWII the transmitter was becoming obsolete because of HF communications equipment taking over, but was put in use as VLF transmitter for submarine communication for Swedish forces. It was finally decommissioned in 1995 and although operating flawlessly, destined for scrapping, no matter that it was the only remaining working piece of its kind in the entire world. The small group of enthusiasts were able to save this fantastic landmark and we have now an opportunity to participate in its annual celebration.

For those equipped with SDR radios extending to VLF range, the exercise is as straightforward as receiving any other station.
For those not having VLF capable receivers in their possession, the following link may be a good starting point: http://www.qsl.net/dl4yhf/speclab/vlf_rcvr.htm

Basically, your favorite SDR software, such as HDSDR, Winrad etc. will do by just connecting a small piece of circuitry in your sound card input. I am not sure if just a long piece of wire (and may be a 17.2kHz bandpass filter) in your microphone input would do it from around the world, but there are reports that it has been working.

[EDIT: In whatever reason, I misposted the SAQ frequency in original post as being 17.9kHz. Now idea where this came from, but the correct one is 17.2kHz as the text now sais. Sorry for the mistake and thanx to IRC user jarod for pointing this out]

SDR MK1 Radio has now Diversity Mode working!

I had people asking me over and over again, why is there no diversity mode for the SDR MK1, if I am using the diversity receiver chipset as the core of the radio ..?!
To be honest ... the idea just did not occur to me! I was so fond of the idea having two radio frontends, that the whole usefulness of diversity mode in urban area did not come to me :)

So, by a popular demand, SDR MK1 is now supporting diversity mode!

For those not familiar with the concept, diversity mode means, that you can use one channel of the radio with your ordinary antenna, while the other channel can be equipped with something receiving a background noise, would it be your own laptop power supply or neighbours plasma TV. The radio then subtracting the noise from useful signal, and you will get noise canceling.

In reality, it looks like that:

(The LO frequency is actually 4.625MHz, the display is just not in sync).

As you see, there is a clear distinction where the diversity mode was switched on and off.  The noise is coming from the halogen kitchen light power supplies in the apartment. The useful signal is received with magnetic loop in the apartment, the noise is received with short telescopic antenna borrowed from ICom scanner.

Please note, that this is not a universal remedy to receive anything from far away - it is not improving any gain, it is just a useful feature to cancel strong local interference sources.

Happy Birthday, Repeater!

It just occurred to me, that UVB-76 Temporary Internet Repeater has a one-year birthday today!
While the first tests were made already on 6'th, the 8'th of June is the date since the repeater has been up and running more or less non-stop.

It has been a rewarding time in every sense and I would like to thank all of you who have gathered around the repeater during this year - you are the best audience one web project could ever wish!